1. Field of the Invention
The present invention relates generally to the assembly of electronic devices. More particularly, the present invention relates to the assembly of radio frequency identification (RFID) straps interposers and/or tags.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. Furthermore the RFID devices include structures to support and protect the antennas and electronics, and to mount or attach them to objects. For example, RFID tags are used in conjunction with security-locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,292, all of which are hereby incorporated by reference in their entireties.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are RFID devices that are adhesively or otherwise attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example by use of a plastic fastener, string or other fastening means. In addition, as discussed below, as an alternative to RFID tags and labels it is possible to mount or incorporate some or all of the antennas and electronics directly on the objects. As used herein, the term “transponders” refers both to RFID devices and to RFID combinations of antennas and analog and/or digital electronics wherein the antenna and/or electronics are mounted directly on the objects.
In many applications the size and shape (form factor) of RFID devices, and mechanical properties such as flexibility, are critical. For reasons such as security, aesthetics, and manufacturing efficiency there is a strong tendency toward smaller form factors. Where thinness and flexibility are desired, it is important to avoid materials (such as bulky electronics) and constructions that add undue thickness or stiffness to the RFID tag or label. RFID devices on the other hand should have adequate electrical connections, mechanical support, and appropriate positioning of the components (chips, chip connectors, antennas). Structures for these purposes can add complexity, thickness and inflexibility to an RFID device.
Another significant form factor, for example in thin flat tags and labels, is the area of the device, and performance requirements of the antenna can affect this area. For example, in the case of a dipole antenna the antenna typically should have a physical length approximately one-half wavelength of the RF device's operating frequency. While the length of this type of antenna may be short for the operating frequency of an RF tag, it may still be larger than many desired RFID device form factors.
In many applications it is desirable to reduce the size of the electronics as small as possible. In order to interconnect very small chips with antennas in RFID inlets, it is known to use a structure variously called “straps”, “interposers”, and “carriers” to facilitate device manufacture. Straps include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling to the antennas. These pads may be used to provide a larger effective electrical contact area than a chip precisely aligned for direct placement without an interposer. The larger area reduces the accuracy required for placement of chips during manufacture while still providing effective electrical connection. Chip placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID strap or interposer structures, typically using a flexible substrate that carries the strap's contact pads or leads. RFID devices incorporating straps or interposers are disclosed, for example, in U.S. Pat. No. 6,606,247 and in European Patent Publication 1 039 543, both of which are incorporated by reference herein in their entireties.
Another consideration is effectiveness of operation of RFID transponders in various operating environments and conditions. For example, operation of an RFID transponder may be affected by the composition of the surface to which it is mounted, the moisture content of the surface to which it is mounted, and various other aspects of an operating environment. Metallic objects in the operating environment, including other RFID transponders, can shift the resonant frequency of an RFID transponder thereby decreasing its effective range. Metallic objects may also reflect an RFID signal, and other objects, such as humans, may absorb RFID signals. Moisture content and/or humidity in the operating environment have further been known to adversely affect RFID transponder performance. While the effects of these materials and operating environment conditions may be avoided by removing them from the RFID operating environment, it is often not practical to do so. For example, when using an RFID transponder to track a package containing a metallic object, it may not be practical to remove the metallic object from the package to facilitate reading the RFID transponder.
Antennas of RFID transponders may be tuned to improve performance in various environments and conditions. One method of tuning an antenna is to provide an antenna with one or more additional conductor portions adjacent to the elements of the antenna. By adjusting the additional conductor portion length, width, and/or spacing distance, and/or the number of conductor portions, the antenna impedance can be changed. This may typically be done mechanically by adding or removing portions of the additional conductor portions and/or by connecting the additional portions with each other and the antenna. By varying the impedance of the antenna, the resonant frequency may be adjusted to compensate for operating environment conditions. However, this method is not well suited for high-speed, low cost implementation of RFID transponders because it may require adding or removing elements of an antenna and manipulation of more than one component.
A known way to form an RFID transponder on an object, such as a package is to mount or form one or more antennas directly on the object, then couple the electronics to the antenna. Various patented combinations of packages with RFID transponders produced in this manner include: U.S. Pat. No. 6,107,920 assigned to Motorola (FIGS. 14 and 15 show a package blank with directly formed antenna, and an RFID circuit chip secured to the package surface); U.S. Pat. No. 6,259,369 assigned to Moore North America (antenna sections printed in conductive ink on a package or envelope, with a label containing an RFID device bridging the antenna sections); and U.S. Pat. No. 6,667,092 assigned to International Paper (capacitive antenna having two pads separated by a gap embedded in packaging linerboard, with an interposer including an RFID processor coupled between the antenna pads). It is also known to incorporate this type of transponder in combination with fabric articles such as clothing, as shown in U.S. Pat. No. 6,677,917 assigned to Philips Electronics. In comparison with the production of RFID devices with antennas and electronics that have been predesigned for improved performance, however, this method of producing RFID transponders on objects suffers the shortcoming that the coupling of the electronics to the antenna may yield sub-optimal, inferior performance.
Therefore, it is desirable to provide a method of making an RFID transponder wherein the configuration of the transponder is dynamically altered to tune a desired characteristic of the transponder in response to various operating environment factors.
From the foregoing it will be seen there is room for improvement of RFID transponders and manufacturing processes relating thereto.